Answer
The monthly cost, $f\left( x \right)$ , for x text messages can be modeled by the function $f\left( x \right)=4+0.15x$.
Work Step by Step
$\text{Monthly cost of text message plan}=\$4$
Now,
$\text{Cost for one text}=\$0.15\text{}$
Now the cost for x text messages will be x times of $\$0.15$
$\text{Cost of }x\text{ text messages}=\$\left(0.15x\right)$
Let $f\left( x \right)$ denotes the monthly cost,
$f\left( x \right)=4+0.15x$
Therefore, the monthly cost, $f\left( x \right)$ , for x text messages can be modeled by the function $f\left( x \right)=4+0.15x$.
